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Eradicating pigs and cats on the Auckland Islands

Introduction

Learn about DOC's work to prepare an eradication plan for pigs and cats on Auckland Island.

Pete McClelland from DOC fitting a satellite transmitter to an Auckland Island pig

Auckland Island has three unwelcome and destructive residents: cats, pigs and mice. While it is not currently feasible to plan for eradicating mice from an island the size of Auckland, pigs and cats are a different story.

Pigs were first introduced to the Auckland Islands in 1807, shortly after the discovery of the island group. There were several later releases, primarily aimed at providing food for castaway sailors, with the last being in the 1890s.

Cats were established by 1840 and so, along with the pigs, would have wiped out many species very early on.

Mice were first recorded in 1851, presumably having got ashore with one of the many sealing gangs which visited the islands or with Hardwicke settlement colonists.

The number of pigs and cats on Auckland Island is unknown, although the pigs are estimated at around 500-1000 (fluctuating depending on how harsh the previous winters were). What is clear though, is that their presence has greatly reduced many species of bird on the island, totally eliminating the ground nesting birds such as flightless teal, snipe and rail, as well as all the burrowing seabirds.

As they are omnivorous, and will eat just about anything that could be considered edible, the pigs have also devastated the island's vegetation and invertebrates. The pigs plough up tussock and other native vegetation to get to edible roots and earthworms, with the damage often obvious for many years. They also rip open any decaying logs to get to the invertebrates and overturn large areas of beach stones in search of kelp fly larvae. Perhaps most dramatically pigs have been seen pushing adult white-capped mollymawks off their nests and eating the eggs and chicks forcing the birds to live only on inaccessible cliffs.

Apart from cats on nearby Masked Island, all the other islands in the Auckland Island group are pig and cat free. Thankfully, most of the bird species that have been eliminated from the main island still survive, albeit in much lower numbers, on one or more of these smaller nearby islands.

In 2007 DOC carried out field trials into the movements and feeding habits of Auckland Island pigs and cats. As part of this, 20 pigs were fitted with satellite transmitters and all the cats within a defined area were caught. Cats are secretive, and rarely seen, and so the trial helped DOC find out how prevalent they were. The information will help DOC prepare an eradication plan that will target the areas frequented by the two species.

While much of the damage pigs and cats have caused is recoverable, it will take decades and come at a hefty price tag. The estimate for an eradication programme for both pigs and cats is about $22m. Techniques are likely to include trapping and aerial and ground hunting over several years.

Ironically, Auckland Island pigs have been found to have a significant economic value. Their isolation for over a century means that they have not been exposed to many of the diseases common to most pig populations. This makes them the preferred candidate for a range of medical research programmes involving transfer of cells to humans.

When the eradication of the Auckland Island pigs was proposed, the Rare Breeds Conservation Society, which aims to preserve the genetics of as many domestic breeds as possible, lead a trip to capture and return pigs to the mainland for a captive breeding programme. This programme proved very successful, and a private company bought animals for their research programme. If required, more animals could be captured prior to the eradication taking place.